1. Field of the Invention
This invention relates to a method of processing the periphery of a silicon-based substrate and a method of manufacturing a semiconductor device based thereon.
2. Background Art
A semiconductor device is manufactured using a semiconductor substrate such as a silicon (Si) substrate and a sequence of multiple steps including lithography, etching, heat treatment (oxidation, annealing, and diffusion), ion implantation, thin film formation (CVD, sputtering, and vapor deposition), and washing (resist removal and washing with solution).
For example, after a nitride film is deposited on a Si substrate, a resist film is applied onto the nitride film and used as a mask to form an opening on the Si substrate by lithography and reactive ion etching. Then a metal film is deposited on the nitride film and heat treated so that the surface of the Si substrate exposed in the opening reacts with the metal to form a silicide film. The unreacted metal film is removed by etching or the like.
However, if the resist film is not sufficiently applied to the periphery of the Si substrate, the Si substrate may be exposed on the periphery when an opening is formed on the Si substrate. If a metal film is deposited and heat treated on the Si substrate being exposed, the Si substrate exposed on the periphery reacts with the metal to produce a silicide film or other reaction product from the metal film and the Si substrate. Unfortunately, this causes metal contamination occurring from the periphery of the Si substrate. To prevent metal contamination, it is known to conduct a process for selectively removing the metal film on the periphery by etching or the like after the silicide film or other reaction product is formed. However, it is difficult to completely remove the silicide film or other reaction product once formed. To prevent the formation of silicide film on the periphery beforehand, it is possible to use a jig called an edge cut ring. However, because this edge cut ring is in contact with the Si substrate, particles are generated from the contact portion and deteriorate the manufacturing yield.
On the other hand, with the enhancement of speed and integration of recent semiconductor devices, there has been a growing trend to use copper (Cu), which has lower electric resistance and higher electromigration tolerance than Al, as a metal material for forming interconnect circuits on a semiconductor substrate. However, there is a concern about Cu contamination of the Si substrate. To prevent Cu contamination of the Si substrate, it is known to conduct a method of forming Cu interconnects after covering the backside and the periphery of the Si substrate with a nitride film beforehand. However, processes such as chemical mechanical polishing (CMP) or reactive ion etching (RIE) in the step of forming Cu interconnects induce the nitride film covering the periphery to be eliminated. If heat treatment is applied while the nitride film is eliminated, Cu diffuses into and contaminates the Si substrate. Thus, to manufacture a semiconductor device with high yield requires protecting the Si substrate against contamination. Various countermeasures for this have been attempted conventionally (see, e.g., JP 6-084887A).